Automobiles equipped with airbags are well known in the prior art. In such airbag systems, the car crash is sensed and the airbags rapidly inflated thereby ensuring the safety of an occupation in a car crash. Many lives have now been saved by such airbag systems.
However, depending on the seated state of an occupant, there are cases where his or her life cannot be saved even by present airbag systems. For example, when a passenger is seated on the front passenger seat in a position other than a forward facing, normal state, e.g., when the passenger is out of position and near the deployment door of the airbag, there will be cases when the occupant will be seriously injured or even killed by the deployment of the airbag.
Also, sometimes a child seat is placed on the passenger seat in a rear facing position and there are cases where a child sitting in such a seat has been seriously injured or killed.
Furthermore, in the case of a vacant seat, there is no need to deploy an airbag, and in such a case, deploying the airbag is undesirable due to a high replacement cost and possible release of toxic gases into the passenger compartment. Nevertheless, most airbag systems will deploy the airbag in a vehicle crash even if the seat is unoccupied.
For these reasons, there has been proposed a seated-state detecting unit such as disclosed in the following U.S. Patents and Patent applications, which are included herein by reference, assigned to the current assignee of the present application: Breed et al (U.S. Pat. No. 5,563,462); Breed et al (U.S. patent application Ser. No. 08/640,068 filed Apr. 30, 1996); Breed et al (U.S. patent application Ser. No. 08/474,783 filed Jun. 7, 1995): Breed et al (U.S. Patent application Ser. No. 08/476,882 filed Jun. 7, 1995; Breed et al (U.S. patent application Ser, No. 08/474,784 filed Jun. 7, 1995; and Varga et al (U.S. patent application Ser. No. 08/798,029 filed Feb. 6, 1997). Typically, in some of these designs four sets of ultrasonic sensors are installed at four points in a vehicle passenger compartment for transmitting ultrasonic or electromagnetic waves toward the passenger or driver's seat and receiving the reflected waves. Using appropriate hardware and software, the approximate configuration of the occupancy of either the passenger or driver seat can be determined thereby identifying and categorizing the occupancy of the relevant seat.
However, in the aforementioned prior art using ultrasonics, the pattern of reflected ultrasonic waves from an adult occupant who may be out of position is sometimes similar to the pattern of reflected waves from a rear facing child seat. Also, it is sometimes difficult to discriminate the wave pattern of a normally seated child with the seat in a rearward position from an empty seat with the seat in a more forward position. In other cases, the reflected wave pattern from a thin slouching adult can be similar to that from a rear facing child seat. In still other cases, the reflected pattern from a passenger seat which is in a forward position can be similar to the reflected wave pattern from a seat containing a forward facing child seat or a child sitting on the passenger seat. In each of these cases, the prior art ultrasonic systems can suppress the deployment of an airbag when deployment is not desired or, alternately, can enable deployment when deployment is desired.
If the discrimination between these cases can be improved, then the reliability of the seated-state detecting unit can be improved and more people saved from death or serious injury. In addition, the unnecessary deployment of an airbag can be prevented.